1. Field of the Invention
The present invention relates to fuel nozzles for gas turbine engines and, more particularly, to a protective sheath assembly for such fuel nozzles.
2. Description of the Prior Art
Fuel nozzles for gas turbine engines are well known in the prior art. Such conventional fuel nozzles are used to supply fuel to a combustion chamber which is provided for igniting the fuel mixture, thereby producing the energy which is used to power the engine. Generally, the combustion chamber includes a plurality of fuel nozzles to thus ensure a proper distribution of the fuel mixture within the combustion chamber.
Conventional fuel nozzles include an inlet fitting, which is coupled to a fuel manifold, and a stem defining a number of fuel passages for directing fuel from the inlet fitting to a tip assembly adapted to atomize the fuel delivered to the combustion chamber. A particular problem with gas turbine fuel nozzles is that the nozzles are located in a hot area of the engine. This heat can cause the fuel passing through the nozzle stem to rise in temperature sufficiently that the fuel can carbonize or coke. Such coking can clog the nozzle and prevent the nozzle from spraying properly. Accordingly, fuel nozzles are typically provided with a protective sheath or heat shield which surrounds the nozzle stem to form an annular air gap thereabout. The sheath and the air gap provide thermal insulation to the fuel nozzle stem in order to prevent the fuel flowing therethrough from coking.
Various methods have been developed to physically attach the protective sheath to the fuel nozzle. For instance, it has been proposed to permanently secure the sheath to the fuel nozzle by brazing or welding the open upper end of the sheath to an enlarged neck provided on the nozzle stem. It has also been proposed to clamp the sheath to the nozzle stem. According to this sheath attachment method, the clamp surrounds the upper end of the sheath to clamp the sheath against the enlarged neck of the nozzle stem. It has also been proposed to secure the sheath to the nozzle stem by means of radial pins extending through the sheath and pressure fitted into the nozzle stem.
The above-described sheath attaching methods are generally of a permanent nature and require the use of tools to install the sheath on the fuel nozzle. It would be highly beneficial to have a non-permanent sheath attaching method and arrangement by which the sheath could be readily installed and removed without requiring any tools.